Increased Aux Tank Capacity

Viperwolf1 · Mar 17, 2010

Got my hands on a spare aux tank from a '73 and figured I'd fix it up to replace mine which leaks a little. First thing I did was measure the capacity. It holds almost 12 gallons when standing on end. I know the rated capacity of a '73 tank is 7.5 gallons but the early years (before venting) held about 11 gallons. So I get to looking inside and figure out why it's only rated at 7.5. It's because the filler vent (1/2" tube) is angled down and ends at about half the tank height. A "full" tank has 4.5 gallons of air trapped in it.

Now I know it needs some extra space for expansion but I figured I could cut this wasted space down by half and still be safe. So I took the vent tube out and drilled some extra holes in the flange to clock the end of the tube up to about 3/4 tank height. You can't simply rotate the tube 90 degrees because the screw holes are offset and it would put the vent at the very top of the tank. By the way the vent tube is sealed with an o-ring and the screws don't go through the inside of the tank. The pictures below show the vent after clocking.

I haven't re-measured yet but it looks like I should be able to get about 9.5 gallons in it now. Not a big difference but it may save me 20-30 miles of walking during my Pony Express trail trip. I still need to modify the float arm to take advantage of the increased capacity.

broncnaz · Mar 17, 2010

The early non vented tank I have on my 73 holds about 10 gallons upon refill. I have a spare tank with the vent tube as well that I plan on replacing the unvented one for easier fill ups good idea. I may be doing the same mod soon. I may have to do my 71 was well.

DAKOTA7720 · Mar 17, 2010

Won't that void the warranty?

Viperwolf1 · Mar 18, 2010

DAKOTA7720 said:
Won't that void the warranty?

Everytime I pickup a tool something is fixing to get voided or mutilated.

Buldozer · Mar 18, 2010

I forget where I got the steel replacement aux tank I am running but it will hold close to 12 gal....

73azbronco · Mar 19, 2010

There's a reason for that open space, a crush zone for side impact. This allows the tank to deform before rupturing and hopefully with the steel plate, deflect fuel down and away from the cab. If the tank is full and it takes a hit, no room for deforming, it pops right then and plumes of fuel who knows where. I may be wrong...

Viperwolf1 · Mar 19, 2010

73azbronco said:
There's a reason for that open space, a crush zone for side impact. This allows the tank to deform before rupturing and hopefully with the steel plate, deflect fuel down and away from the cab. If the tank is full and it takes a hit, no room for deforming, it pops right then and plumes of fuel who knows where. I may be wrong...

You may very well be right. The tank capacity was reduced back in the time of the Pinto fireballs. I'll take my chances with it though.

I did get to measure the modified capacity yesterday and it took just short 9.5 gallons until liquid started coming out of the vent tube.

76 bronco J · Mar 19, 2010

>>>> side fuel tanks outside the frame rails are a bad idea no matter how you look at it & the reason I just added a larger rear tank instead of going that route........ remember all the crap GM got into on the subject >>[youtube]<object width="660" height="525"><param name="movie" value="http://www.youtube.com/v/RqpOyiIx8n4&hl=en_US&fs=1&rel=0&color1=0xe1600f&color2=0xfebd01&border=1"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="http://www.youtube.com/v/RqpOyiIx8n4&hl=en_US&fs=1&rel=0&color1=0xe1600f&color2=0xfebd01&border=1" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="660" height="525"></embed></object>[/youtube]

DirtDonk · Mar 19, 2010

Although I agree, do you remember how the video footage in the old news stories (not this one in the video) was rigged with movie incendiaries to achieve the "desired effect" though?
The reporters got called on that one when someone saw the initial flare (they used a small solid-fuel rocket motor if I remember) underneath the tank just before it erupted in flame.
The leak was there from the accident no doubt, but they just had to go and "fan the flames" so to speak, to get more spectacular air-time out of it. Kind of like shooting yourself in the foot to make the point that a gun can be dangerous in the wrong hands?

Not that anyone would do such a thing, of course...

Paul

Viperwolf1 · Mar 23, 2010

I added a fuel return port to the tank sender. There are only a few places where the extra port can go due to the body brace blocking most of the sender face. The tube is soldered in securely but I'm going to add some epoxy for good measure. I still need to extend the float arm a few inches to make up for the increased capacity then I'll button it up, install it, and see if I can make it leak.

ken75ranger · Mar 24, 2010

Nice work.

phred · Mar 24, 2010

As alway Viper, nice work. Looks like another mod I need to add to the list. this would make a good tech article.

broncnaz · Mar 24, 2010

76 bronco J said:
>>>> side fuel tanks outside the frame rails are a bad idea no matter how you look at it & the reason I just added a larger rear tank instead of going that route........ remember all the crap GM got into on the subject

Sure lots of things are bad ideas broncos and most other trucks out there all have side tanks granted most are inside the frame now. But what happens when the driveshaft lets go? More recently crown vics had issues with there rear tank catching fire when a car would impact the rear of the parked crown vic while traveling 60 miles a hour.
There are lots of "bad" ideas lifts, big tires, poor brakes, speeding, overdriving your rig,

Accidents happen plain and simple some if not most are preventable just by driver awareness. My whole take on driving is not to get into a accident vehicle safety to me is it should be safe during normal driving once you get into a accident then anything can and will happen no matter what safety features are built in. If cars were 100% safe then nobody would ever die in a accident in todays cars.

Viperwolf1 · Mar 25, 2010

I extended the float arm about 1.5" using 1/8" brass tubing from a hobby store. I expoxied the inside of the sender tubes and electrical connector in case of pinhole leaks in the solder. I also picked up a new gasket from the Ford dealer, C0AF-9276-A for $1.03.

I had to put a slight bend in the tube so the float wouldn't bottom out on the tank. I ran a piece of solder into the tube before bending so I wouldn't kink it. When the tank is full the float arm is now long enough to reach the fuel level. Now with a total of almost 33 gallons I should have a highway cruising range of about 500 miles.

Teal68 · Sep 10, 2013

Wow! 3 very nice and clean modifications. Thanks for the link on the other thread.

bteutsch · Dec 22, 2021

Been looking for this thread!!!!

DirtDonk · Dec 22, 2021

Your search kung fu is strong today!

Rustytruck · Dec 22, 2021

Add some heavy wall sliders under the rockers and you now have inside the rails protection for side impact. people worry to much. reminds me of 100 ways to die in the west. Just stay out of the fair and you will be OK.

Broncobowsher · Dec 22, 2021

11+ year old thread with the last post over 8 years ago...
Pulled from the archives, kicked back into life. Well not really, kicked back into recently read anyway.
Time for a nap, let it sleep for another decade, see who wakes it later.

bteutsch · Dec 22, 2021

DirtDonk said:
Your search kung fu is strong today!

Hey Paul, don’t ask how long that took.. I searched every way I could think of and finally just looked at every post of Viperwolf’s until I found it..

Increased Aux Tank Capacity

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